Various techniques have been used for welding plastic tubes particularly as used in the medical field. U.S. Pat. No. 7,398,813 describes a device having a first tube holder and a second tube holder. Each of the tube holders has first and second parallel tube holding areas in line with each other. In practice a first tube would be placed in the aligned first tube holding areas across the location where the tube holders are adjacent each other. A second tube would be similarly placed in the aligned second tube holding areas. A tube clamp in each of the first tube holding areas clamps the first tube to create a generally fluid free area of the first tube. A tube clamp is similarly provided in the second tube holding areas to create a generally fluid free area of the second tube. One of the tube holders is laterally movable while the clamps are maintained in their clamping condition. To increase the length of the fluid free area, the laterally movable tube holder is laterally shifted while the clamps are closed. Such movement is performed after the tubes are initially loaded in a loading station, and when the tube holders are in a stripping station. Thereafter, the tubes are cut. In U.S. Pat. No. 7,398,813 the cutting is done with a non-heated cutting device, such as a cold blade, and the tube holders are then moved to a heating station while the clamps are still maintained in their clamping condition, In the heating station a heating device heats/melts the cut stub ends of the tubes. The cut ends of the tubes are realigned so that a cut stub end of the first tube becomes aligned with a cut stub end of the second tube and these two aligned heated/melted cut stub ends are then shifted into contact with each other to become welded together.
When the clamps are being closed in the loading station, the movable tube holder is forced against the fixed tube holder by a spring. The welding device of U.S. Pat. No. 7,398,813 works effectively where the tubing used is within the specific tube thickness for which the clamps were sized. If, however, a tubing of greater tube thickness is used, the spring force may not be sufficient to keep the clamp faces flush when the tubing is compressed during loading. Instead, the extra material of the thick tubing may become expressed out from the clamp faces and cause separation of the spring loaded clamps. This could trap fluid between the clamp faces. In such circumstance this would defeat the purpose of the later stripping process and could create conditions for weak welds.